Some endrotracheal tubes (ETTs) comprise an inflatable cuff, which forms a seal against the tracheal wall. This seal prevents gases from leaking past the cuff and allows positive pressure ventilation. Desired safe inflatable cuff pressure is in the range of 23-27 cm H2O, with an optimal pressure of about 25 cm H2O. Pressure above 30 cm H2O can cause irritation to the surrounding tracheal tissue. Extended duration of such high cuff pressure can interfere with oxygen flow to the tissue, causing tissue necrosis and a substantial wound. Low cuff pressure, typically below 20 cm H2O, compromises the cuff sealing performance, and allows leakage into the lungs of subglottic fluids descending from above the cuff.
The external surface of inflatable cuffs is in communication with the ventilation pressure of the lungs. The pressure of the inflatable cuff cycles with the ventilation cycle. When an artificially-ventilated patient is also anesthetized, the plastic of the inflatable cuff absorbs the nitrous oxide (N2O) gas used in anesthesia, which increases pressure in the cuff.
In current clinical settings of intensive care patients, changes of body positioning lead to significant changes in cuff pressure in the range of 10-50 cm H2O, i.e., out of the safe range of 20-30 cm H2O, and certainly out of the desired range of 23-27 cm H2O. See, for example, Lizy C et al., “Cuff pressure of endrotracheal tubes after changes in body position in critically ill patients treated with mechanical ventilation,” Am J Crit Care. 2014 January; 23(1):e1-8.
Therefore, there is a need to safely maintain the inflatable cuff pressure is in the range of 23-27 cm H2O, optimally about 25 cm H2O, and to avoid extended periods of pressure above 30 cm H2O. In particular, there is a need to suppress the fluctuations of pressure in clinical settings caused by patient change of body positions.
Currently, the most common practiced approach for ETT cuff pressure management is manual monitoring (using a manometer) and adjustment of cuff pressure, which contributes to ICU staff workload. It has been shown that up to eight manual adjustments of cuff pressure are required daily to maintain recommended cuff pressure ranges. Even so, the cuff pressure is uncontrolled during the long time periods between manual cuff adjustments. In addition, the manometer must be connected to and disconnected from the ETT cuff for each pressure measurement, which allows a small amount of air to escape from the ETT cuff. Still further, many conventional ETT manometers lose calibration relatively quickly.
Prior art cuff pressure regulators can be divided into two groups: (a) large bedside non-disposable expensive electric pump and electronic pressure monitors: and (b) small and light disposable non-electric limited-pressure reservoir compartments that must be filled manually. Use of disposable devices both prevents cross-contamination between patients and obviates the need for costly sterilization processes between patients. Moreover, the compactness of the disposable devices allows them to be attached on the ETT circuit and not occupy bedside space and an electric power cable connection.
Laryngeal mask airway (LMA) devices are useful in facilitating lung ventilation by forming a low-pressure seal around the patient's laryngeal inlet, thereby avoiding the known harmful effects of ETT devices, which form a seal within the trachea. LMA devices have become standard medical devices, instead of ETT devices, for rapidly and reliably establishing an unobstructed airway in a patient in emergency situations and in the administration of anesthetic gases.
During general anesthesia, pulmonary ventilation is secured with an ETT device or by an LMA device, and attention to the risk of complications related to a high intracuff pressure is important. When the cuff-to-tracheal wall pressure exceeds the tracheal capillary pressure (130-140 cm H2O) for approximately 15 minutes, the tracheal mucous membrane becomes ischemic. The intracuff pressure approximates the cuff-to-tracheal wall pressures in high volume/low pressure cuffs, and a cuff pressure below 120 cm H2O is recommended to prevent ischemic injury. In addition, recurrent laryngeal nerve palsy has been demonstrated in up to 5% of patients after intubation, and a high cuff pressure is suspected as contributing to this complication. Similarly, in patients provided with a laryngeal mask, a high cuff pressure may lead to palsy of the lingual, hypoglossal, and recurrent laryngeal nerves, and postoperative sore throat.
US Patent Application Publication 2015/0283343 to Schnell et al. describes a pressure-equalizing device with a pressure equalizing balloon, the volume of which is connected to a further volume, the pressure of which is intended to be kept at as constant a value as possible even in the event of an enforced change in volume. In order therefore to keep the cuff pressure within the pressure range that is generally considered to be useful and optimal of between approximately 20 mbar and 30 mbar, but also make possible, if required, to increase the pressure in a controlled manner, according to the invention the equalizing balloon keeping the pressure generally constant is accommodated in a protective sleeve which has radial bulges deviating from a uniformly concave form matched to the outer contour of the balloon, which bulges are designed such that the equalizing balloon first abuts against the wall areas of the protective sleeve matched to the contour of the balloon and then, when pressure is increased, extends only into the bulges, whereby the pressure in the equalizing balloon gradually increases as the volume in the bulges increases.
PCT Publication WO 2017/153988 to Zachar et al., which is incorporated herein by reference, describes a cuff pressure stabilizer that includes an inflation lumen proximal port connector, which is shaped to form an air-tight seal with an inflation lumen proximal port of a catheter additionally having an inflatable cuff and an inflation lumen; a fluid reservoir; a liquid column container, which is (a) open to the atmosphere at at least one site along the liquid column container, (b) in fluid communication with the fluid reservoir, and (c) in communication with the inflation lumen proximal port connector via the fluid reservoir: and a liquid, which is contained (a) in the fluid reservoir, (b) in the liquid column container, or (c) partially in the fluid reservoir and partially in the liquid column container, and which has a density of between 1.5 and 5 g/cm3 at 4 degrees Celsius at 1 atm.